Cytokine activation of p38 mitogen-activated protein kinase and apoptosis is opposed by alpha-4 targeting of protein phosphatase 2A for site-specific dephosphorylation of MEK3

GqPCR-stimulated dephosphorylation of AKT is induced by an IGBP1-mediated PP2A switch

BACKGROUND

G protein-coupled receptors (GPCRs) usually regulate cellular processes via activation of intracellular signaling pathways. However, we have previously shown that in several cell lines, GqPCRs induce immediate inactivation of the AKT pathway, which leads to JNK-dependent apoptosis. This apoptosis-inducing AKT inactivation is essential for physiological functions of several GqPCRs, including those for PGF2α and GnRH.

METHODS

Here we used kinase activity assays of PI3K and followed phosphorylation state of proteins using specific antibodies. In addition, we used coimmunoprecipitation and proximity ligation assays to follow protein-protein interactions. Apoptosis was detected by TUNEL assay and PARP1 cleavage.

RESULTS

We identified the mechanism that allows the unique stimulated inactivation of AKT and show that the main regulator of this process is the phosphatase PP2A, operating with the non-canonical regulatory subunit IGBP1. In resting cells, an IGBP1-PP2Ac dimer binds to PI3K, dephosphorylates the inhibitory pSer608-p85 of PI3K and thus maintains its high basal activity. Upon GqPCR activation, the PP2Ac-IGBP1 dimer detaches from PI3K and thus allows the inhibitory dephosphorylation. At this stage, the free PP2Ac together with IGBP1 and PP2Aa binds to AKT, causing its dephosphorylation and inactivation.

CONCLUSION

Our results show a stimulated shift of PP2Ac from PI3K to AKT termed "PP2A switch" that represses the PI3K/AKT pathway, providing a unique mechanism of GPCR-stimulated dephosphorylation. Video Abstract.

MicroRNA-214 in Health and Disease

MicroRNAs (miRNAs) are endogenously expressed, non-coding RNA molecules that mediate the post-transcriptional repression and degradation of mRNAs by targeting their 3′ untranslated region (3′-UTR). Thousands of miRNAs have been identified since their first discovery in 1993, and miR-214 was first reported to promote apoptosis in HeLa cells. Presently, miR-214 is implicated in an extensive range of conditions such as cardiovascular diseases, cancers, bone formation and cell differentiation. MiR-214 has shown pleiotropic roles in contributing to the progression of diseases such as gastric and lung cancers but may also confer cardioprotection against excessive fibrosis and oxidative damage. These contrasting functions are achieved through the diverse cast of miR-214 targets. Through silencing or overexpressing miR-214, the detrimental effects can be attenuated, and the beneficial effects promoted in order to improve health outcomes. Therefore, discovering novel miR-214 targets and understanding how miR-214 is dysregulated in human diseases may eventually lead to miRNA-based therapies. MiR-214 has also shown promise as a diagnostic biomarker in identifying breast cancer and coronary artery disease. This review provides an up-to-date discussion of miR-214 literature by describing relevant roles in health and disease, areas of disagreement, and the future direction of the field.

Comparative transcriptome provides insights into the selection adaptation between wild and farmed foxes

The silver fox and blue fox are economically important fur species and were domesticated by humans from their wild counterparts, the arctic fox and red fox, respectively. Farmed foxes show obvious differences from their wild counterparts, including differences in physiology, body size, energy metabolism, and immunity. However, the molecular mechanisms underlying these differences are presently unclear. In this study, we built transcriptome libraries from multiple pooled tissues for each species of farmed fox, used RNA-seq to obtain a comprehensive dataset, and performed selection analysis and sequence-level analyses of orthologous genes to identify the genes that may be influenced by human domestication. More than 153.3, 248.0, 81.6, and 65.8 million clean reads were obtained and assembled into a total of 118,577, 401,520, 79,900, and 186,988 unigenes with an average length range from 521 to 667 bp for AF, BF, RF, and SF, respectively. Selective pressure analysis showed that 11 and 14 positively selected genes were identified, respectively, in the two groups (AF vs. BF and RF vs. SF). Several of these genes were associated with natural immunity (CFI and LRRFIP1), protein synthesis (GOLGA4, CEP19 and SLC35A2), and DNA damage repair (MDC1). Further functional enrichment analyses demonstrated that two positively selected genes (ACO1 and ACAD10) were involved in metabolic process (GO:0008152, p-value = .032), representing a significant enrichment. Sequence analysis of 117 orthologous genes shared by the two groups showed that the LEMD2, RRBP1, and IGBP1 genes might be affected by artificial selection in farmed foxes, with mutation sites located within sequences that are otherwise highly conserved across most mammals. Our results provide a valuable transcriptomic resource for future genetic studies and improvement in the assisted breeding of foxes and other farmed animals.

Merkel cell polyomavirus small tumour antigen activates the p38 MAPK pathway to enhance cellular motility

Merkel cell carcinoma (MCC) is an aggressive skin cancer with high rates of recurrence and metastasis. Merkel cell polyomavirus (MCPyV) is associated with the majority of MCC cases. MCPyV-induced tumourigenesis is largely dependent on the expression of the small tumour antigen (ST). Recent findings implicate MCPyV ST expression in the highly metastatic nature of MCC by promoting cell motility and migration, through differential expression of cellular proteins that lead to microtubule destabilisation, filopodium formation and breakdown of cell-cell junctions. However, the molecular mechanisms which dysregulate these cellular processes are yet to be fully elucidated. Here, we demonstrate that MCPyV ST expression activates p38 MAPK signalling to drive cell migration and motility. Notably, MCPyV ST-mediated p38 MAPK signalling occurs through MKK4, as opposed to the canonical MKK3/6 signalling pathway. In addition, our results indicate that an interaction between MCPyV ST and the cellular phospatase subunit PP4C is essential for its effect on p38 MAPK signalling. These results provide novel opportunities for the treatment of metastatic MCC given the intense interest in p38 MAPK inhibitors as therapeutic agents.

Transcriptome Profiling Reveals Pro-Inflammatory Cytokines and Matrix Metalloproteinase Activation in Zika Virus Infected Human Umbilical Vein Endothelial Cells

The deformities in the newborns infected with Zika virus (ZIKV) present a new potential public health threat to the worldwide community. Although ZIKV infection is mainly asymptomatic in healthy adults, infection during pregnancy can cause microcephaly and other severe brain defects and potentially death of the fetus. The detailed mechanism of ZIKV-associated damage is still largely unknown; however, it is apparent that the virus crosses the placental barrier to reach the fetus. Endothelial cells are the key structural component of the placental barrier. Endothelium integrity as semi-permeable barrier is essential to control the molecules and leukocytes trafficking across the placenta. Damaged endothelium or disruption of adherens junctions could compromise endothelial barrier integrity causing leakage and inflammation. Endothelial cells are often targeted by viruses, including the members of the Flaviviridae family such as dengue virus (DENV) and West Nile virus (WNV); however, little is known about the effects of ZIKV infection of endothelial cell functions. Our transcriptomic data have demonstrated that the large number of cytokines is affected in ZIKV-infected endothelial cells, where significant changes in 13 and 11 cytokines were identified in cells infected with PRVABC59 and IBH30656 ZIKV strains, respectively. Importantly, these cytokines include chemokines attracting mononuclear leukocytes (monocytes and lymphocytes) as well as neutrophils. Additionally, changes in matrix metalloproteinase (MMPs) were detected in ZIKV-infected cells. Furthermore, we for the first time showed that ZIKV infection of human umbilical vein endothelial cells (HUVECs) increases endothelial permeability. We reason that increased endothelial permeability was due to apoptosis of endothelial cells caused by caspase-8 activation in ZIKV-infected cells.

Bacillus anthracis Edema Toxin Inhibits Efferocytosis in Human Macrophages and Alters Efferocytic Receptor Signaling

The Bacillus anthracis Edema Toxin (ET), composed of a Protective Antigen (PA) and the Edema Factor (EF), is a cellular adenylate cyclase that alters host responses by elevating cyclic adenosine monophosphate (cAMP) to supraphysiologic levels. However, the role of ET in systemic anthrax is unclear. Efferocytosis is a cAMP-sensitive, anti-inflammatory process of apoptotic cell engulfment, the inhibition of which may promote sepsis in systemic anthrax. Here, we tested the hypothesis that ET inhibits efferocytosis by primary human macrophages and evaluated the mechanisms of altered efferocytic signaling. ET, but not PA or EF alone, inhibited the efferocytosis of early apoptotic neutrophils (PMN) by primary human M2 macrophages (polarized with IL-4, IL-10, and/or dexamethasone) at concentrations relevant to those encountered in systemic infection. ET inhibited Protein S- and MFGE8-dependent efferocytosis initiated by signaling through MerTK and αVβ5 receptors, respectively. ET inhibited Rac1 activation as well as the phosphorylation of Rac1 and key activating sites of calcium calmodulin-dependent kinases CamK1α, CamK4, and vasodilator-stimulated phosphoprotein, that were induced by the exposure of M2(Dex) macrophages to Protein S-opsonized apoptotic PMN. These results show that ET impairs macrophage efferocytosis and alters efferocytic receptor signaling.

Inflammation and pharmacokinetics: potential implications for HIV-infection

INTRODUCTION

The physiological changes accompanying inflammation may alter the pharmacokinetics (PK) of certain medications. Individuals infected with HIV have chronically elevated inflammatory markers despite viral suppression following effective antiretroviral therapy (ART), as well as age-related inflammation. Understanding the potential clinical implications of inflammation on the PK of medications is important for understanding dose-response relationships and necessitates future research. Areas covered: An extensive literature search was carried out using PubMed and associated bibliographies to summarize the current state of knowledge regarding altered PK in response to inflammation and its application to the field of HIV. Expert opinion: Preclinical and clinical studies show that inflammation leads to a downregulation of certain drug metabolizing enzymes and both up and down regulation of transporters depending on the transporter and cell type. Decreased gastric acidity, fluid shifts, and plasma protein alterations also occur with inflammation, leading to potential absorption, distribution, and clearance changes. More research is needed including controlled PK studies to address the clinical relevance of these observations, especially in the aging HIV-infected population. Results from future studies will enable us to better predict drug concentrations in individuals with inflammation, in line with efforts to provide personalized pharmacotherapy in our healthcare system.

Multiplexed Fluorescent Immunodetection Using Low Autofluorescence Immobilon®-FL Membrane

By enabling greater signal linearity and multiplexed detection, fluorescent western immunodetection overcomes many of the inherent technical limitations associated with the traditional chemiluminescent detection method. However, the sensitivity of fluorescence detection can be severely compromised by high background autofluorescence of various blotting membranes. Here, we describe a low autofluorescence PVDF membrane (Immobilon(®)-FL membrane) optimized for fluorescent immunodetection, and we report its use in the quantitative fluorescent western immunodetection of biomarkers associated with Alzheimer's disease (AD). First, membrane autofluorescence of four different commercially available blotting membranes was compared. Immobilon(®)-FL membrane exhibited the lowest autofluorescence with substantially increased detection sensitivity. We also show that the fluorescent immunodetection exhibited greatly increased linear dynamic range (two orders of magnitude, log scale) compared to the traditional chemiluminescent methods (less than one order of magnitude). Immobilon(®)-FL membrane was then used to quantify the expression levels of previously reported biomarkers associated with AD (synaptophysin, GSK3β, and GAP43). Total protein extracts from age-matched brain samples of three AD patients and three normal controls were used. Biomarker expression levels were normalized to that of a housekeeping protein (GAPDH) using multiplexed detection, conserving difficult-to-obtain biological tissue samples and minimizing experimental variation. We found that the expression of GSK3ß and GAP43 biomarkers were significantly reduced in AD brain samples compared to age-matched normal samples. In summary, combining fluorescent immunodetection with a low autofluorescent blotting membrane yields accurate and reliable multiplexed quantitation of AD biomarkers. While this report focuses on the quantitation of AD biomarkers, the described technique is applicable to comparing protein expression in other biological contexts as well.

PP2A as a master regulator of the cell cycle

Protein phosphatase 2A (PP2A) plays a critical multi-faceted role in the regulation of the cell cycle. It is known to dephosphorylate over 300 substrates involved in the cell cycle, regulating almost all major pathways and cell cycle checkpoints. PP2A is involved in such diverse processes by the formation of structurally distinct families of holoenzymes, which are regulated spatially and temporally by specific regulators. Here, we review the involvement of PP2A in the regulation of three cell signaling pathways: wnt, mTOR and MAP kinase, as well as the G1→S transition, DNA synthesis and mitotic initiation. These processes are all crucial for proper cell survival and proliferation and are often deregulated in cancer and other diseases.

Basal protein phosphatase 2A activity restrains cytokine expression: role for MAPKs and tristetraprolin

PP2A is a master controller of multiple inflammatory signaling pathways. It is a target in asthma; however the molecular mechanisms by which PP2A controls inflammation warrant further investigation. In A549 lung epithelial cells in vitro we show that inhibition of basal PP2A activity by okadaic acid (OA) releases restraint on MAPKs and thereby increases MAPK-mediated pro-asthmatic cytokines, including IL-6 and IL-8. Notably, PP2A inhibition also impacts on the anti-inflammatory protein - tristetraprolin (TTP), a destabilizing RNA binding protein regulated at multiple levels by p38 MAPK. Although PP2A inhibition increases TTP mRNA expression, resultant TTP protein builds up in the hyperphosphorylated inactive form. Thus, when PP2A activity is repressed, pro-inflammatory cytokines increase and anti-inflammatory proteins are rendered inactive. Importantly, these effects can be reversed by the PP2A activators FTY720 and AAL(s), or more specifically by overexpression of the PP2A catalytic subunit (PP2A-C). Moreover, PP2A plays an important role in cytokine expression in cells stimulated with TNFα; as inhibition of PP2A with OA or PP2A-C siRNA results in significant increases in cytokine production. Collectively, these data reveal the molecular mechanisms of PP2A regulation and highlight the potential of boosting the power of endogenous phosphatases as novel anti-inflammatory strategies to combat asthmatic inflammation.

Impact of deoxynivalenol (DON) contaminated feed on intestinal integrity and immune response in swine

This study was performed to characterize the influence of consuming DON naturally contaminated feeds on pig's intestinal immune defenses, antibody response and cellular immunity. Sixteen 4-week-old piglets were randomly allocated to two dietary treatments: control diet or diet contaminated with 3.5 mg DON/kg. At days 7 and 21, animals were immunized with ovalbumin (OVA). On day 42, intestinal samples were collected for measurement of gene expression involved in immune response, oxidative status and barrier function. Primary IgG antibody response to OVA was increased in pigs fed DON diet compared to control animals. In the ileum of pigs fed DON diet, claudin, occludin, and vimentin genes involved in integrity and barrier function were down-regulated compared to controls. Results also revealed that expression of two chemokines (IL-8, CXCL10), interferon-γ, and major antioxidant glutathione peroxidase 2 (GPX-2) were up-regulated whereas expression of genes encoding enzymatic antioxidants including GPX-3, GPX-4 and superoxide dismutase 3 (SOD-3) were down-regulated in pigs fed DON-contaminated diet. These results strongly suggest that ingestion of DON naturally contaminated feed impaired intestinal barrier and immunological functions by modulating expression of genes coding for proteins involved in tight junctions, tissue remodelling, inflammatory reaction, oxidative stress reaction and immune response.

Tristetraprolin and its role in regulation of airway inflammation

Chronic inflammatory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are clinically and socioeconomically important diseases globally. Currently the mainstay of anti-inflammatory therapy in respiratory diseases is corticosteroids. Although corticosteroids have proven clinical efficacy in asthma, many asthmatic inflammatory conditions (e.g., infection, exacerbation, and severe asthma) are not responsive to corticosteroids. Moreover, despite an understanding that COPD progression is driven by inflammation, we currently do not have effective anti-inflammatory strategies to combat this disease. Hence, alternative anti-inflammatory strategies are required. p38 mitogen-activated protein kinase (MAPK) has emerged as an important signaling molecule driving airway inflammation, and pharmacological inhibitors against p38 MAPK may provide potential therapies for chronic respiratory disease. In this review, we discuss some of the recent in vitro and in vivo studies targeting p38 MAPK, but suggest that p38 MAPK inhibitors may prove less effective than originally considered because they may block anti-inflammatory molecules along with proinflammatory responses. We propose that an alternative strategy may be to target an anti-inflammatory molecule farther downstream of p38 MAPK, i.e., tristetraprolin (TTP). TTP is an mRNA-destabilizing, RNA-binding protein that enhances the decay of mRNAs, including those encoding proteins implicated in chronic respiratory diseases. We suggest that understanding the molecular mechanism of TTP expression and its temporal regulation will guide future development of novel anti-inflammatory pharmacotherapeutic approaches to combat respiratory disease.

Lysine methylation in cancer: SMYD3-MAP3K2 teaches us new lessons in the Ras-ERK pathway

Lysine methylation has been traditionally associated with histones and epigenetics. Recently, lysine methyltransferases and demethylases - which are involved in methylation of non-histone substrates - have been frequently found deregulated in human tumours. In this realm, a new discovery has unveiled the methyltransferase SMYD3 as an enhancer of Ras-driven cancer. SMYD3 is up-regulated in different types of tumours. SMYD3-mediated methylation of MAP3K2 increases mutant K-Ras-induced activation of ERK1/2. Methylation of MAP3K2 prevents it from binding to the phosphatase PP2A, thereby impeding the impact of this negative regulator on Ras-ERK1/2 signals, leading to the formation of lung and pancreatic adenocarcinomas. Furthermore, depletion of SMYD3 synergises with a MEK inhibitor, currently in clinical trials, to block Ras-driven pancreatic neoplasia. These results underscore the importance of lysine methylation in the regulation of signalling pathways relevant for tumourigenesis and endorse the development of drugs targeting unregulated lysine methylation as therapeutic agents in the struggle against cancer.

MLK3 is part of a feedback mechanism that regulates different cellular responses to reactive oxygen species

Reactive oxygen species (ROS) influence diverse cellular processes, including proliferation and apoptosis. Both endogenous and exogenous ROS activate signaling through mitogen-activated proteins kinase (MAPK) pathways, including those involving extracellular signal-regulated kinases (ERKs) or c-Jun N-terminal kinases (JNKs). Whereas low concentrations of ROS generally stimulate proliferation, high concentrations result in cell death. We found that low concentrations of ROS induced activating phosphorylation of ERKs, whereas high concentrations of ROS induced activating phosphorylation of JNKs. Mixed lineage kinase 3 (MLK3, also known as MAP3K11) directly phosphorylates JNKs and may control activation of ERKs. Mathematical modeling of MAPK networks revealed a positive feedback loop involving MLK3 that determined the relative phosphorylation of ERKs and JNKs by ROS. Cells exposed to an MLK3 inhibitor or cells in which MLK3 was knocked down showed increased activation of ERKs and decreased activation of JNKs and were resistant to cell death when exposed to high concentrations of ROS. Thus, the data indicated that MLK3 is a critical factor controlling the activity of kinase networks that control the cellular responses to different concentrations of ROS.

Differential effects of nitrostyrene derivatives on myelopoiesis involve regulation of C/EBPα and p38MAPK activity

Bone marrow failure syndromes and MDS represent a heterogenous group of diseases, characterized by ineffective myelopoiesis, the risk of clonal evolution and a generally poor response to chemotherapy-based treatment regimen. Nitrostyrene derivatives have been studied as protein phosphatase inhibitors in various tumor models. Pharmacological studies have identified nitrostyrene as the structural core underlying a pro-apoptotic effect in tumor cells, yet their effects on normal cells, including those of the hematopoietic system, are largely unknown. In this study, utilizing umbilical cord blood-derived myeloid progenitor cells, patient-derived bone marrow cells, and a (BALB/c) mouse model; we investigated the effects of treatment with two nitrostyrene derivatives (NTS1 and NTS2) on myeloid development. We demonstrate that these compounds stimulate the expansion and differentiation of myeloid progenitors in vitro and improve myeloid reconstitution after chemotherapy-induced bone marrow depletion in vitro and in vivo. These effects were accompanied by increased C/EBPα expression and activity and inhibition of the p38MAPK signalling pathway. Together, our data suggest that nitrostyrenes improve myelopoiesis and represent potential new treatment strategies for patients suffering from bone marrow failure syndromes, hypocellular myelodysplastic syndrome and chemotherapy-induced aplasia.

A small molecule, MTBT, prevents cancer cell growth by activating p38 MAPK

Cancer is a disease of unscheduled cell division and many anticancer drugs target the cell cycle to inhibit the proliferation of cancer cells. We conducted a screen for new anticancer drugs that induce cell cycle arrest using a small compound library. From this screen, we identified 2-(3-methyl-thiophen-2-yl)-4-(3,4-dioxybenzene) thiazole (MTBT), which causes accumulation of cancer cells with 4N DNA content and inhibits colony formation of several cancer cell lines. We further showed that the treatment of cancer cells with this compound for a longer time period leads to apoptosis, as indicated by the presence of cells with a sub-G1 peak and the appearance apoptotic markers. The increased phosphorylation of serine 10 on histone H3 in MTBT-treated cancer cells suggests cell cycle arrest in the M-phase. Strikingly, MTBT-induced cell cycle arrest and enhanced H3 (Ser10) phosphorylation are abrogated by the pretreatment with SB203580, a specific inhibitor of mitogen-activated protein kinase p38. Moreover, treatment of cancer cells with MTBT induces the phosphorylation of p38, indicative of p38 activation. Together, we have identified a new compound that inhibits cancer cell proliferation, which is likely a consequence of p38 activation.

HIV-1 Tat-mediated induction of CCL5 in astrocytes involves NF-κB, AP-1, C/EBPα and C/EBPγ transcription factors and JAK, PI3K/Akt and p38 MAPK signaling pathways

The incidence of HIV-associated neurological disorders (HAND) has increased during recent years even though the highly active antiretroviral therapy (HAART) has significantly curtailed the virus replication and increased the life expectancy among HIV-1 infected individuals. These neurological deficits have been attributed to HIV proteins including HIV-1 Tat. HIV-1 Tat is known to up-regulate CCL5 expression in mouse astrocytes, but the mechanism of up-regulation is not known. The present study was undertaken with the objective of determining the mechanism(s) underlying HIV-1 Tat-mediated expression of CCL5 in astrocytes. SVGA astrocytes were transiently transfected with a plasmid encoding Tat, and expression of CCL5 was studied at the mRNA and protein levels using real time RT-PCR and multiplex cytokine bead array, respectively. HIV-1 Tat showed a time-dependent increase in the CCL5 expression with peak mRNA and protein levels, observed at 1 h and 48 h post-transfection, respectively. In order to explore the mechanism(s), pharmacological inhibitors and siRNA against different pathway(s) were used. Pre-treatment with SC514 (NF-κB inhibitor), LY294002 (PI3K inhibitor), AG490 (JAK2 inhibitor) and Janex-1 (JAK3 inhibitor) showed partial reduction of the Tat-mediated induction of CCL5 suggesting involvement of JAK, PI3K/Akt and NF-κB in CCL5 expression. These results were further confirmed by knockdown of the respective genes using siRNA. Furthermore, p38 MAPK was found to be involved since the knockdown of p38δ but not other isoforms showed partial reduction in CCL5 induction. This was further confirmed at transcriptional level that AP-1, C/EBPα and C/EBPγ were involved in CCL5 up-regulation.

Androgen receptor (AR) differential roles in hormone-related tumors including prostate, bladder, kidney, lung, breast and liver

The androgen receptor (AR) is expressed in many cell types and the androgen/AR signaling has been found to have important roles in modulating tumorigenesis and metastasis in several cancers including prostate, bladder, kidney, lung, breast and liver. However, whether AR has differential roles in the individual cells within these tumors that contain a variety of cell types remains unclear. Generation of AR knockout (ARKO) mouse models with deletion of AR in selective cells within tumors indeed have uncovered many unique AR roles in the individual cell types during cancer development and progression. This review will discuss the results obtained from various ARKO mice and different human cell lines with special attention to the cell type- and tissue-specific ARKO models. The understanding of various results showing the AR indeed has distinct and contrasting roles in each cell type within many hormone-related tumors (as stimulator in bladder, kidney and lung metastases vs as suppressor in prostate and liver metastases) may eventually help us to develop better therapeutic approaches by targeting the AR or its downstream signaling in individual cell types to better battle these hormone-related tumors in different stages.

PPE38 of Mycobacterium marinum triggers the cross-talk of multiple pathways involved in the host response, as revealed by subcellular quantitative proteomics

The PE/PPE family of proteins which are in high abundance in pathogenic species such as Mycobacterium tuberculosis and M. marinum, play the critical role in generating antigenic variation and evasion of host immune responses. However, little is known about their functional roles in mycobacterial pathogenesis. Previously, we found that PPE38 is associated with the virulence of mycobacteria, presumably by modulating the host immune response. To clarify the link between PPE38 and host response, we employed a subcellular, amino acid-coded mass tagging (AACT)/SILAC-based quantitative proteomic approach to determine the proteome changes during host response to M. marinum PPE38. As a result, 291 or 290 proteins were found respectively to be up- or down-regulated in the nucleus. Meanwhile, 576 upregulated and 272 downregulated proteins were respectively detected in the cytosol. The data of quantitative proteomic changes and concurrent biological validations revealed that M. marinum PPE38 could trigger extensive inflammatory responses in macrophages, probably through interacting with toll-like receptor 2 (TLR2). We also found that PPE38 may arrest MHC-1 processing and presentation in infected macrophages. Using bioinformatics tools to analyze global changes in the host proteome, we obtained a PPE38-respondor network involved in various transcriptional factors (TFs) and TF-associated proteins. The results of our systems investigation now indicate that there is cross-talk involving a broad range of diverse biological pathways/processes that coordinate the host response to M. marinum PPE38.

Role of plasminogen activator inhibitor-1 in urokinase's paradoxical in vivo tumor suppressing or promoting effects

Tumor proteases and inhibitors have been associated with paradoxical effects on tumor progression in preclinical and clinical settings. We previously reported that urokinase (uPA) overexpression delays tumor progression in mammary cancer. This study aimed to determine the role of plasminogen activator inhibitor-1 (PAI-1) on uPA's paradoxical in vivo effects. Using syngeneic murine models, we found that stable uPA overexpression promoted in vivo growth of colon tumors (MC-38) naturally expressing high PAI-1, whereas growth inhibition was observed in renal tumors (RENCA) expressing lower PAI-1 levels. In murine mammary carcinoma (4T1), uPA overexpression shifted the uPA/PAI-1 balance in favor of the protease, resulting in significantly reduced tumor growth and metastases in vivo. Conversely, increased tumor progression was observed in stable PAI-1 overexpressing 4T1 tumors as compared with uPA-overexpressing and control tumors. These effects were associated with downregulation of metastases promoting genes in uPA-overexpressing tumors, such as metalloproteinases, CXCL-1, c-Fos, integrin α-5, VEGF-A, PDGF-α, and IL-1β. In PAI-1-overexpressing tumors, many of the above genes were upregulated. PAI-1 overexpressing tumors had increased total and new tumor microvessels, and increased tumor cell proliferation, whereas the opposite effects were found in uPA-overexpressing tumors. Finally, PAI-1 downregulation led to significant inhibition of 4T1 tumor growth and metastases in vivo. In conclusion, uPA's dual effects on tumor progression occur in the context of its interactions with endogenous PAI-1 expression. Our studies uncover novel mechanisms of in vivo tumor control by modulation of the balance between tumor proteases and inhibitors, which may be exploited therapeutically.

A dual role for receptor-interacting protein kinase 2 (RIP2) kinase activity in nucleotide-binding oligomerization domain 2 (NOD2)-dependent autophagy

Autophagy is triggered by the intracellular bacterial sensor NOD2 (nucleotide-binding, oligomerization domain 2) as an anti-bacterial response. Defects in autophagy have been implicated in Crohn's disease susceptibility. The molecular mechanisms of activation and regulation of this process by NOD2 are not well understood, with recent studies reporting conflicting requirements for RIP2 (receptor-interacting protein kinase 2) in autophagy induction. We examined the requirement of NOD2 signaling mediated by RIP2 for anti-bacterial autophagy induction and clearance of Salmonella typhimurium in the intestinal epithelial cell line HCT116. Our data demonstrate that NOD2 stimulates autophagy in a process dependent on RIP2 tyrosine kinase activity. Autophagy induction requires the activity of the mitogen-activated protein kinases MEKK4 and p38 but is independent of NFκB signaling. Activation of autophagy was inhibited by a PP2A phosphatase complex, which interacts with both NOD2 and RIP2. PP2A phosphatase activity inhibited NOD2-dependent autophagy but not activation of NFκB or p38. Upon stimulation of NOD2, the phosphatase activity of the PP2A complex is inhibited through tyrosine phosphorylation of the catalytic subunit in a process dependent on RIP2 activity. These findings demonstrate that RIP2 tyrosine kinase activity is not only required for NOD2-dependent autophagy but plays a dual role in this process. RIP2 both sends a positive autophagy signal through activation of p38 MAPK and relieves repression of autophagy mediated by the phosphatase PP2A.

Novel Ser/Thr protein phosphatases in cell death regulation

Cell death is regulated by a myriad of intracellular molecular pathways, with many involving protein phosphorylation and dephosphorylation. In this review, we will focus on Ser/Thr phosphatases-mediated regulation in cell apoptosis as well as on their potential roles in cell necrosis. The emerging functional importance of Ser/Thr protein phosphatases in cell death regulation adds new dimension to the signaling mechanisms of cellular function, physiology, and diseases.

The biogenesis of active protein phosphatase 2A holoenzymes: a tightly regulated process creating phosphatase specificity

Protein phosphatase type 2A (PP2A) enzymes constitute a large family of Ser/Thr phosphatases with multiple functions in cellular signaling and physiology. The composition of heterotrimeric PP2A holoenzymes, resulting from the combinatorial assembly of a catalytic C subunit, a structural A subunit, and regulatory B-type subunit, provides the essential determinants for substrate specificity, subcellular targeting, and fine-tuning of phosphatase activity, largely explaining why PP2A is functionally involved in so many diverse physiological processes, sometimes in seemingly opposing ways. In this review, we highlight how PP2A holoenzyme biogenesis and enzymatic activity are controlled by a sophisticatedly coordinated network of five PP2A modulators, consisting of α4, phosphatase 2A phosphatase activator (PTPA), leucine carboxyl methyl transferase 1 (LCMT1), PP2A methyl esterase 1 (PME-1) and, potentially, target of rapamycin signaling pathway regulator-like 1 (TIPRL1), which serve to prevent promiscuous phosphatase activity until the holoenzyme is completely assembled. Likewise, these modulators may come into play when PP2A holoenzymes are disassembled following particular cellular stresses. Malfunctioning of these cellular control mechanisms contributes to human disease. The potential therapeutic benefits or pitfalls of interfering with these regulatory mechanisms will be briefly discussed.

A MID1 gene mutation in a patient with Opitz G/BBB syndrome that altered the 3D structure of SPRY domain

Mutations in the MID1 gene result in X-linked Opitz G/BBB syndrome (OS), a disorder that affects development of midline structures and comprises hypertelorism, cleft lip/palate, hypospadias, and laryngo-tracheo-esophageal abnormalities, and, at times, neurological, anal, and cardiac defects. MID1 gene abnormalities include missense, nonsense, and splicing mutations, small insertions, small deletions, and complex rearrangements. Here, we present a patient with Opitz G/BBB syndrome and a unique MID1 gene point mutation c.1703T Collapse

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MESH Headings

• Abnormalities, Multiple/genetics
• Base Sequence
• Carrier Proteins/genetics
• Chromosome Disorders/genetics
• Esophagus/abnormalities
• Humans
• Hypertelorism/genetics
• Hypospadias/genetics
• Infant, Newborn
• Male
• Microtubule Proteins/genetics
• Nuclear Proteins/genetics
• Point Mutation
• Polymerase Chain Reaction/methods
• Protein Structure, Tertiary
• Sequence Alignment
• Sequence Analysis, DNA
• Transcription Factors/genetics
• Tripartite Motif Proteins
• Ubiquitin-Protein Ligases

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Affiliation(s)

Ching-Hsuan Hu Department of Pediatrics, Chung Shan Medical University Hospital, Taichung, Taiwan
Yu-Fan Liu
Ju-Shan Yu
Yan-Yan Ng
Suh-Jen Chen
Pen-Hua Su
Jia-Yuh Chen

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Identifying putative candidate genes and pathways involved in immune responses to porcine reproductive and respiratory syndrome virus (PRRSV) infection

Differences in gene expression were compared between RNAs from lungs of high (HR) and low (LR) porcine reproductive and respiratory syndrome virus (PRRSV) burden pigs using the swine protein-annotated long oligonucleotide microarray, the Pigoligoarray. Pathway analyses were carried out to determine biological processes, pathways and networks that differ between the LR and HR responses. Differences existed between HR and LR pigs for 16 signalling pathways [P < 0.01/-log (P-value) >1.96]. Top canonical pathways included acute phase response signalling, crosstalk between dendritic cells and natural killer cells and tight junction signalling, with numerous immune response genes that were upregulated (SOCS1, SOD2, RBP4, HLA-B, HLA-G, PPP2R1A and TAP1) or downregulated (IL18, TF, C4BPA, C1QA, C1QB and TYROBP). One mechanism, regulation of complement activation, may have been blocked in HR (PRRSV-susceptible) pigs and could account for the poor clearance of PRRSV by infected macrophages. Multiple inhibiting signals may have prevented effective immune responses in susceptible HR pigs, although some protective genes were upregulated in these pigs. It is likely that in HR pigs, expression of genes associated with protection was delayed, so that the immune response was not stimulated early; thus, PRRSV infection prevented protective immune responses.

Microcystin-LR (MCLR) induces a compensation of PP2A activity mediated by α4 protein in HEK293 cells

Protein phosphatase 2A (PP2A) is a major protein phosphatase with important cell functions. Known and utilized as a potent inhibitor of PP2A, microcystin-LR (MCLR) targets PP2A as a core element that affects numerous cellular mechanisms. But apart from direct inhibition, the exact effect of MCLR on PP2A in cell is largely unknown, specifically with regard to cellular response and autoregulation. Here, we show that a low concentration of MCLR stimulates, rather than inhibits, PP2A activity in HEK293 cells. Immunoprecipitation and immunofluorescence assays reveal that the catalytic subunit and a regulatory subunit of PP2A, termed α4, dissociate from inactive complex upon MCLR exposure, suggesting that the released catalytic subunit regains activity and thereby compensates the activity loss. At high concentrations of MCLR, PP2A activity decreases along with dissociation of the core enzyme and altered post-translational modification of its catalytic subunit. In addition, the dissociation of α4 and PP2A may contribute to destabilization of HEK293 cells cytoskeleton architecture, detachment to extracellular matrix and further anoikis. Our data provide a novel PP2A upregulation mechanism and challenge the recognition of MCLR only as a PP2A inhibitor in cells.

The role of cytokines in the regulation of drug disposition: extended functional pleiotropism?

INTRODUCTION

Drug disposition, metabolism and drug-drug interactions are important considerations for most drugs. Cytokines are integral to the successful resolution of many diseases. Data are emerging on a role for cytokines in regulation of the expression and activity of drug transporters and drug metabolising enzymes. Investigation of the interaction between pharmacological and immunological responses is key to understanding the complex relationships involved in patient response to therapy.

AREAS COVERED

Evidence detailing the ability of cytokines to regulate drug disposition and metabolism is reviewed in the context of different cell and tissue types. The literature search undertaken provides an overview of the current understanding of the interrelationship between pharmacological and immunological factors which may influence successful drug therapy.

EXPERT OPINION

Dysregulation of cytokines and cytokine networks is a hallmark of a number of diseases such as HIV and cancer. The mechanisms by which the immune system can influence drug disposition are relatively understudied but recent work has highlighted the necessity for examining its impact on pharmacokinetics and pharmacodynamics. A more comprehensive approach in clinical studies will allow better determination of the impact of cytokines on drug disposition. In addition, determining the mechanisms that underpin the differential effects of cytokines across different cell types will clarify the responses reported in these studies.

Comprehensive analysis of phosphorylation sites in Tensin1 reveals regulation by p38MAPK

Tensin1 is the archetype of a family of focal adhesion proteins. Tensin1 has a phosphotyrosine binding domain that binds the cytoplasmic tail of β-integrin, a Src homology 2 domain that binds focal adhesion kinase, p130Cas, and the RhoGAP called deleted in liver cancer-1, a phosphatase and tensin homology domain that binds protein phosphatase-1α and other regions that bind F-actin. The association between tensin1 and these partners affects cell polarization, migration, and invasion. In this study we analyzed the phosphorylation of human S-tag-tensin1 expressed in HEK293 cells by mass spectrometry. Peptides covering >90% of the sequence initially revealed 50 phosphorylated serine/phosphorylated threonine (pSer/pThr) but no phosphorylated tyrosine (pTyr) sites. Addition of peroxyvanadate to cells to inhibit protein tyrosine phosphatases exposed 10 pTyr sites and addition of calyculin A to cells to inhibit protein phosphatases type 1 and 2A gave a total of 62 pSer/pThr sites. We also characterized two sites modified by O-linked N-acetylglucosamine. Tensin1 F302A, which does not bind protein phosphatase-1, showed > twofold enhanced phosphorylation of seven sites. The majority of pSer/pThr have adjacent proline (Pro) residues and we show endogenous p38 mitogen activated protein kinase (MAPK) associated with and phosphorylated tensin1 in an in vitro kinase assay. Recombinant p38α MAPK also phosphorylated S-tag-tensin1, resulting in decreased binding with deleted in liver cancer-1. Activation of p38 MAPK in cells by sorbitol-induced hyperosmotic stress increased phosphorylation of S-tag-tensin1, which reduced binding to deleted in liver cancer-1 and increased binding to endogenous pTyr proteins, including p130Cas and focal adhesion kinase. These data demonstrate that tensin1 is extensively phosphorylated on Ser/Thr residues in cells and phosphorylation by p38 MAPK regulates the specificity of the tensin1 Src homology 2 domain for binding to different proteins. Tensin1 provides a hub for connecting signaling pathways involving p38 MAP kinase, tyrosine kinases and RhoGTPases.

Protein phosphatase 2A carboxymethylation and regulatory B subunits differentially regulate mast cell degranulation

Asthma is characterised by antigen-mediated mast cell degranulation resulting in secretion of inflammatory mediators. Protein phosphatase 2A (PP2A) is a serine/threonine protein phosphatase composed of a catalytic (PP2A-C) subunit together with a core scaffold (PP2A-A) subunit and a variable, regulatory (PP2A-B) subunit. Previous studies utilising pharmacological inhibition of protein phosphatases have suggested a positive regulatory role for PP2A in mast cell degranulation. In support of this we find that a high okadaic acid concentration (1μM) inhibits mast cell degranulation. Strikingly, we now show that a low concentration of okadaic acid (0.1μM) has the opposite effect, resulting in enhanced degranulation. Selective downregulation of the PP2A-Cα subunit by short hairpin RNA also enhanced degranulation of RBL-2H3 mast cells, suggesting that the primary role of PP2A is to negatively regulate degranulation. PP2A-B subunits are responsible for substrate specificity, and carboxymethylation of the PP2A-C subunit alters B subunit binding. We show here that carboxymethylation of PP2A-C is dynamically altered during degranulation and inhibition of methylation decreases degranulation. Moreover downregulation of the PP2A-Bα subunit resulted in decreased MK2 phosphorylation and degranulation, whilst downregulation of the PP2A-B'δ subunit enhanced p38 MAPK phosphorylation and degranulation. Taken together these data show that PP2A is both a positive and negative regulator of mast cell degranulation, and this differential role is regulated by carboxymethylation and specific PP2A-B subunit binding.

Mammalian target of rapamycin in spinal cord neurons mediates hypersensitivity induced by peripheral inflammation

mTOR, the mammalian target of rapamycin, is a serine-threonine kinase known to regulate cell proliferation and growth. mTOR has also been implicated in neuronal synaptic plasticity as well as in pain transmission in models of chemically induced and neuropathic pain. To date, the role of mTOR as a modulator of inflammatory pain has not been examined. In this study, we investigated the role of mTOR in Sprague-Dawley rats using the carrageenan model of inflammatory pain. mRNA of Ras homolog enriched in brain (Rheb), a GTPase that positively regulates mTOR activation, was significantly increased 2 h following carrageenan injection. Four hours after induction of inflammation phosphorylation (p) of p70S6 kinase (S6K), ribosomal protein S6 (S6) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) was increased, indicating mTOR activation. Inhibition of spinal mTOR with intrathecal (i.t.) injection of rapamycin (0.1-3 microg) led to a dose-dependent decrease in carrageenan-induced thermal hyperalgesia and a reduction of mechanical allodynia. In vitro studies confirmed rapamycin inhibition of the mTOR pathway. Carrageenan-induced activation of the mTOR pathway in rats was localized predominantly to dorsal horn neurons in the superficial lamina. Taken together, these data show that the mTOR pathway is activated in dorsal horn neurons during inflammatory pain, and that inhibition of spinal mTOR attenuates inflammation-induced thermal and tactile hypersensitivity. Hence, our study indicates that spinal mTOR is an important regulator of spinal sensitization and suggests that targeting mTOR may provide a new avenue for pain therapy.

Lack of Mid1, the mouse ortholog of the Opitz syndrome gene, causes abnormal development of the anterior cerebellar vermis

Opitz G/BBB syndrome (OS) is a genetic disorder characterized by midline developmental defects. Male patients with the X-linked form of OS, caused by loss-of-function mutations in the MID1 gene, show high variability of the clinical signs. MID1 encodes a ubiquitin ligase that controls phosphatase 2A, but its role in the pathogenesis of the disease is still unclear. Here, we report a mouse line carrying a nonfunctional ortholog of the human MID1 gene, Mid1. Mid1-null mice show the brain anatomical defect observed in patients (i.e., hypoplasia of the anterior portion of the medial cerebellum, the vermis). We found that the presence of this defect correlates with motor coordination and procedural and nonassociative learning impairments. The defect is limited to the most anterior lobes of the vermis, the region of the developing cerebellum adjacent to the dorsal midbrain. Analyses at midgestation reveal that lack of Mid1 causes the shortening of the posterior dorsal midbrain, the rostralization of the midbrain/cerebellum boundary, and the downregulation of a key player in the development of this region, Fgf17. Thus, lack of Mid1 causes a misspecification of the midbrain/cerebellar boundary that results in an abnormal development of the most anterior cerebellar lobes. This animal model provides a tool for additional in vivo studies of the physiological and pathological role of the Mid1 gene and a system to investigate the development and function of anterior cerebellar domains.

MicroRNA-214 is aberrantly expressed in cervical cancers and inhibits the growth of HeLa cells

MicroRNAs are a group of endogenously expressed, single-stranded, 18-24 nt RNAs that regulate diverse cellular pathways. Although documented evidence indicates that some microRNAs can function as oncogenes or tumor-suppressors, the role of miR-214 in regulating human cervical cancer cells remains unexplored. We determined the expression level of miR-214 and found it is downregulated in cervical cancer compared with normal tissue. Overexpression of miR-214 in HeLa cells, a human cervical cancer cell line, significantly inhibited cell proliferation according to the MTT and colony forming assays. HeLa cells that stably overexpress miR-214 downregulate the expression of MEK3 and JNK1 at both mRNA and protein levels. Further investigation revealed that miR-214 regulates the expression of MEK3 and JNK1 by targeting the 3'UTRs of these genes. Collectively, these results suggest that miR-214 negatively regulates HeLa cell proliferation by targeting the noncoding regions of MEK3 and JNK1 mRNAs.

Kinases and phosphatases in ischaemic preconditioning: a re-evaluation

Activation of several protein kinases occurs during myocardial ischaemia and during subsequent reperfusion. In contrast to the intensive investigation into the significance of kinase activation in cardioprotection, relatively little is known about the role of the phosphatases in this regard. The aim of this study was to re-evaluate the putative roles of PP1 and PP2A in ischaemia/reperfusion and in triggering ischaemic preconditioning. Isolated perfused working rat hearts were subjected to sustained global (15 or 20 min) or regional ischaemia (35 min), followed by reperfusion. Hearts were preconditioned using global ischaemia (1 x 5 or 3 x 5 min, alternated with 5 min reperfusion). To inhibit both PP1 and PP2A cantharidin (5 muM) was used. To inhibit PP2A only, okadaic acid (7.5 nM) was used. The drugs were administered during the preconditioning protocol, before onset of sustained ischaemia (pretreatment) or during reperfusion. Endpoints were mechanical recovery during reperfusion, infarct size and activation of PKB/Akt, p38 MAPK and ERK p42/p44, as determined by Western blot. Pretreatment of hearts with okadaic acid or cantharidin caused a significant reduction in mechanical recovery after 15 or 20 min global ischaemia. Administration of the drugs during an ischaemic preconditioning protocol abolished functional recovery during reperfusion and significantly increased infarct size. Administration of the drugs during reperfusion had no deleterious effects and increased functional recovery in 3 x PC hearts. To find an explanation for the differential effects of the inhibitors depending on the time of administration, hearts were freeze-clamped at different time points during the perfusion protocol. Administration of cantharidin before 5 min ischaemia activated all kinases. Subsequent reperfusion for 5 min without the drug maintained activation of the kinases until the onset of sustained ischaemia. Cantharidin given during preconditioning was associated with activation of p38MAPK and PKB/Akt during reperfusion after sustained ischaemia. However, administration of the drug during reperfusion only after sustained ischaemia caused activation of both PKB/Akt and ERK p42/p44. Phosphatase inhibition immediately prior to the onset of sustained ischaemia or during preconditioning abolishes protection during reperfusion, while inhibition of these enzymes during reperfusion either had no effect or enhanced the cardioprotective effects of preconditioning. It is proposed that inhibition of phosphatases during reperfusion may prolong the period of RISK activation and hence protect the heart.

Chemokine receptors CXCR4 and CCR7 promote metastasis by preventing anoikis in cancer cells

Chemokine receptors are essential mediators of the metastatic spread in various cancer types; however their precise function in the development of secondary tumors remains poorly understood. We report here a novel property of the chemokine receptors CXCR4 and CCR7 in inhibiting detachment-induced cell death--anoikis, which is believed to be one of the major blocks in the metastatic spread of various neoplasms. Activation of these chemokine receptors by their respective ligands, CXCL12 and CCL21 specifically reduced the sensitivity of metastatic breast cancer cells to anoikis by a distinct mechanism of selective regulation of pro-apoptotic Bmf and anti-apoptotic Bcl-xL proteins. Consequently, functional CXCR4 and CCR7 increased cell survival in the absence of correct ECM attachment both in vitro and in vivo. We also demonstrated that preventing chemokine-induced reduction in Bmf levels significantly attenuated breast cancer metastasis in an experimental mouse model. These results provide evidence for a previously unknown axis in malignant tumors, which connects chemokine receptors with deregulated apoptosis in the absence of the appropriate cell--ECM interaction and may offer novel targets for therapeutic intervention for the treatment of metastatic breast and potentially other tumors.

Vaccinia virus WR53.5/F14.5 protein is a new component of intracellular mature virus and is important for calcium-independent cell adhesion and vaccinia virus virulence in mice

The vaccinia virus WR53.5L/F14.5L gene encodes a small conserved protein that was not detected previously. However, additional proteomic analyses of different vaccinia virus isolates and strains revealed that the WR53.5 protein was incorporated into intracellular mature virus (IMV). The WR53.5 protein contains a putative N-terminal transmembrane region and a short C-terminal region. Protease digestion removed the C terminus of WR53.5 protein from IMV particles, suggesting a similar topology to that of the IMV type II transmembrane protein. We generated a recombinant vaccinia virus, vi53.5L, that expressed WR53.5 protein under isopropyl-beta-d-thiogalactopyranoside (IPTG) regulation and found that the vaccinia virus life cycle proceeded normally with or without IPTG, suggesting that WR53.5 protein is not essential for vaccinia virus growth in cell cultures. Interestingly, the C-terminal region of WR53.5 protein was exposed on the cell surface of infected cells and mediated calcium-independent cell adhesion. Finally, viruses with inactivated WR53.5L gene expression exhibited reduced virulence in mice when animals were inoculated intranasally, demonstrating that WR53.5 protein was required for virus virulence in vivo. In summary, we identified a new vaccinia IMV envelope protein, WR53.5, that mediates cell adhesion and is important for virus virulence in vivo.

Vasoinhibins prevent retinal vasopermeability associated with diabetic retinopathy in rats via protein phosphatase 2A-dependent eNOS inactivation

Increased retinal vasopermeability contributes to diabetic retinopathy, the leading cause of blindness in working-age adults. Despite clinical progress, effective therapy remains a major need. Vasoinhibins, a family of peptides derived from the protein hormone prolactin (and inclusive of the 16-kDa fragment of prolactin), antagonize the proangiogenic effects of VEGF, a primary mediator of retinal vasopermeability. Here, we demonstrate what we believe to be a novel function of vasoinhibins as inhibitors of the increased retinal vasopermeability associated with diabetic retinopathy. Vasoinhibins inhibited VEGF-induced vasopermeability in bovine aortic and rat retinal capillary endothelial cells in vitro. In vivo, vasoinhibins blocked retinal vasopermeability in diabetic rats and in response to intravitreous injection of VEGF or of vitreous from patients with diabetic retinopathy. Inhibition by vasoinhibins was similar to that achieved following immunodepletion of VEGF from human diabetic retinopathy vitreous or blockage of NO synthesis, suggesting that vasoinhibins inhibit VEGF-induced NOS activation. We further showed that vasoinhibins activate protein phosphatase 2A (PP2A), leading to eNOS dephosphorylation at Ser1179 and, thereby, eNOS inactivation. Moreover, intravitreous injection of okadaic acid, a PP2A inhibitor, blocked the vasoinhibin effect on endothelial cell permeability and retinal vasopermeability. These results suggest that vasoinhibins have the potential to be developed as new therapeutic agents to control the excessive retinal vasopermeability observed in diabetic retinopathy and other vasoproliferative retinopathies.

Protein phosphatase 2A regulatory subunits and cancer

The serine/threonine protein phosphatase (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of a number of major signaling pathways whose deregulation can contribute to cancer. The specificity and activity of PP2A are highly regulated through the interaction of a family of regulatory B subunits with the substrates. Accumulating evidence indicates that PP2A acts as a tumor suppressor. In this review we summarize the known effects of specific PP2A holoenzymes and their roles in cancer relevant pathways. In particular we highlight PP2A function in the regulation of MAPK and Wnt signaling.

Type I interferon-dependent and -independent expression of tripartite motif proteins in immune cells

The tripartite motif (TRIM) proteins are important in a variety of cellular functions additional to anti-viral activity. We systematically analysed mRNA expression of representative TRIM molecules in mouse macrophages, myeloid and plasmacytoid dendritic cells, and a selection of CD4(+) T cell subsets. We defined four clusters of TRIM genes based on their selective expression in these cells. The first group of TRIM genes was preferentially expressed in CD4(+) T cells and contained the COS-FN3 motif previously shown to be involved in protein interactions. Additional TRIM genes were identified that showed up-regulation in macrophages and dendritic cells upon influenza virus infection in a type I IFN-dependent manner, suggesting that they have anti-viral activity. In support of this notion, a subset of these TRIM molecules mapped to mouse chromosome 7, syntenic to human chromosome 11, where TRIM family members such as TRIM5, shown to have anti-viral activity, are localized. A distinct group of TRIM was constitutively expressed in plasmacytoid dendritic cells independently of viral infection or signalling through the type I IFN receptor. Our findings on expression and regulation of TRIM genes in cells of the immune system that have different effector functions in innate and adaptive immune responses, may provide leads for determining functions of this diverse family of molecules.

TAB4 stimulates TAK1-TAB1 phosphorylation and binds polyubiquitin to direct signaling to NF-kappaB

Responses to transforming growth factor beta and multiple cytokines involve activation of transforming growth factor beta-activated kinase-1 (TAK1) kinase, which activates kinases IkappaB kinase (IKK) and MKK3/6, leading to the parallel activation of NF-kappaB and p38 MAPK. Activation of TAK1 by autophosphorylation is known to involve three different TAK1-binding proteins (TABs). Here we report a protein phosphatase subunit known as type 2A phosphatase-interacting protein (TIP) that also acts as a TAB because it co-precipitates with and directly binds to TAK1, enhances TAK1 autophosphorylation at unique sites, and promotes TAK1 phosphorylation of IKKbeta and signaling to NF-kappaB. Mass spectrometry demonstrated that co-expression of TAB4 protein significantly increased phosphorylation of four sites in TAK1, in a linker region between the kinase and TAB2/3 binding domains, and two sites in TAB1. Recombinant GST-TAB4 bound in an overlay assay directly to inactive TAK1 and activated TAK1 but not TAK1 phosphorylated in the linker sites, suggesting a bind and release mechanism. In kinase assays using TAK1 immune complexes, added GST-TAB4 selectively stimulated IKK phosphorylation. TAB4 co-precipitated polyubiquitinated proteins dependent on a Phe-Pro motif that was required to enhance phosphorylation of TAK1. TAB4 mutated at Phe-Pro dominantly interfered with IL-1beta activation of NF-kappaB involving IKK-dependent but not p38 MAPK-dependent signaling. The results show that TAB4 binds TAK1 and polyubiquitin chains to promote specific sites of phosphorylation in TAK1-TAB1, which activates IKK signaling to NF-kappaB.

MID1 mutations in patients with X-linked Opitz G/BBB syndrome

Mutations in the MID1 gene are responsible for the X-linked form of Opitz G/BBB syndrome (OS), a disorder that affects the development of midline structures. OS is characterized by hypertelorism, hypospadias, laryngo-tracheo-esophageal (LTE) abnormalities, and additional midline defects. Cardiac, anal, and neurological defects are also present. The expressivity of OS is highly variable, even within the same family. We reviewed all the MID1 mutations reported so far, in both familial and sporadic cases. The mutations are scattered along the entire length of the gene and consist of missense and nonsense mutations, insertions and deletions, either in-frame or causing frameshifts, and deletions of either single exons or the entire MID1 coding region. The variety of described mutations and the lack of a strict genotype-phenotype correlation confirm the previous suggestion of the OS phenotype being caused by a loss-of-function mechanism. However, although a specific mutation cannot entirely account for the observed phenotype, we observed preferential association between some types of mutation and specific clinical manifestations, e.g., brain anatomical defects and truncating mutations. This may suggest that the pathogenetic mechanism underlying the OS phenotype is more complex and may vary among the affected organs.

The structure of Tap42/alpha4 reveals a tetratricopeptide repeat-like fold and provides insights into PP2A regulation

Physiological functions of protein phosphatase 2A (PP2A) are determined via the association of its catalytic subunit (PP2Ac) with diverse regulatory subunits. The predominant form of PP2Ac assembles into a heterotrimer comprising the scaffolding PR65/A subunit together with a variable regulatory B subunit. A distinct population of PP2Ac associates with the Tap42/alpha4 subunit, an interaction mutually exclusive with that of PR65/A. Tap42/alpha4 is also an interacting subunit of the PP2Ac-related phosphatases, PP4 and PP6. Tap42/alpha4, an essential protein in yeast and suppressor of apoptosis in mammals, contributes to critical cellular functions including the Tor signaling pathway. Here, we describe the crystal structure of the PP2Ac-interaction domain of Saccharomyces cerevisiae Tap42. The structure reveals an all alpha-helical protein with striking similarity to 14-3-3 and tetratricopeptide repeat (TPR) proteins. Mutational analyses of structurally conserved regions of Tap42/alpha4 identified a positively charged region critical for its interactions with PP2Ac. We propose a scaffolding function for Tap42/alpha4 whereby the interaction of PP2Ac at its N-terminus promotes the dephosphorylation of substrates recruited to the C-terminal region of the molecule.